It is well known in the video signal processing arts that the quality of reproduced images from transmitted video signals can be significantly enhanced through the use of temporal signal processing. Such temporal signal processing may take the form of field/frame comb filtering, field/frame recursive filtering for noise reduction and interlaced to non-interlaced scan conversion to name a few examples. It is also known that interframe image motion tends to introduce artifacts in temporally processed video signals. These artifacts may be rendered substantially unperceptible if the temporal processing apparatus is made adaptive responsive to image motion. Hence the need for apparatus to detect image movement.
A large variety of motion detection apparatus has been proposed. The majority of such apparatus determine differences between video signals separated by one frame interval. These interframe difference signals are processed in various methods to develop a resultant motion signal. U.S. Pat. Nos. 4,811,092 and 4,794,454 show examples of this type of motion detector.
In general, the one frame motion detectors do not provide satisfactory motion indication signals. It has been determined that more accurate motion detection may be effected by simultaneously analyzing signal differences between several fields or frames. For example, M. Achiha et al. of the Central Research Laboratory of Hitachi Ltd., in a paper entitled "Movement Detection in NTSC Color TV Signals" (PCS86 Tokyo), describes a method wherein a plurality of pixel values from two fields of a first frame are summed to produce a first average; a plurality of pixel values from two fields of the next adjacent exclusive frame are summed to produce a second average; and, the first and second averages are differenced to produce a raw motion signal which then undergoes further processing.
U.S. Pat. No. 4,626,891 shows motion detection apparatus utilizing signal from four consecutive fields wherein three frame differences are determined. One of the frame differences is temporally displaced from the other two by a field interval. The three differences are scaled and summed to generate a raw motion signal which thereafter undergoes further processing.
Nominally, the above mentioned apparatus operate on luminance and chrominance signals that have been separated from a composite video signal. However, perfect luminance/chrominance separation cannot be achieved. Residual cross components in either of the separated signals tend to introduce errors in motion signals developed by the prior art motion detection apparatus.
It is an object of the present invention to provide an improved image motion detection apparatus. One feature of the invention is less susceptibility to generating errors resulting from cross components when detecting image motion in separated luminance component signals.